Like the pyogenic bacteria, viruses produce local lesions and may also cause a widespread reaction to the infection such as erythema multiforme.
However, the clinical manifestations of common viral infections of the skin are easily recognised.
Local infective lesions caused by DNA viruses which can be isolated from the lesions themselves include the herpes and pox virus groups.
In patients with AIDS chronic and widespread viral infections of the skin occur.
Herpes
Herpes simplex
The herpes simplex virus consists of two viral subtypes. Type I is associated with lesions on the face and fingers and sometimes genital lesions. Type II is associated almost entirely with genital infections.
Recurrent episodes of infection are common, with both due to latent infection of sensory nerve ganglia.
Primary herpes simplex (type I) infection usually occurs in or around the mouth, with variable involvement of the face. Lesions are small vesicles which crust over and heal but there may be considerable malaise.
Type II infection affects the external genitalia and waist area.
Recurrent infections are shorter lived (three to five days), occur in the distribution of a sensory nerve on the face or genitalia, and may be triggered by a variety of stimuli from sunlight to febrile illness.
Herpes zoster
Varicella zoster virus (VZV) causes both chickenpox, the primary illness, and herpes zoster, which follows reactivation of the virus in the nerve ganglia.
In zoster, pain, fever, and malaise may occur before erythematous papules develop in the area of the affected dermatome most commonly in the thoracic area.
Vesicles develop over several days, crusting over as they resolve.
Secondary bacterial infection is common.
Some patients develop episodes of pain in the affected area postherpetic neuralgia after clearance of the rash. Skin lesions and nasopharyngeal secretions can transmit chickenpox. Treatment
Localised lesions of herpes simplex have been treated with a variety of medications from zinc sulphate to iodoxuridine.
Topical acyclovir a drug that inhibits herpes virus DNA polymerase is effective but only shortens the duration of illness by a day or so.
It is useful in primary infection but should be used as soon as the patient is aware of symptoms.
Severe, recurrent, herpes simplex, or herpes zoster can be treated with oral or intravenous aciclovir as early in the course of the illness as possible.
Ganciclovir is an alternative.
Secondary infection may require antiseptic soaks, such as 1/1000 potassium permanganate, or topical or systemic antibiotics.
Steroids (prednisolone 40–60 mg/day) given during the acute stage of herpes zoster may diminish pain and postherpetic neuralgia.
Rest and analgesics are recommended treatment for extensive herpes simplex or herpes zoster infections.
Pox viruses
The pox viruses are large DNA viruses, with a predilection for the epidermis.
Variola (smallpox), once a disease with high mortality, has been eliminated by vaccination with modified vaccinia (cowpox) virus.
Molluscum contagiosum
The commonest skin infection due to a pox virus is molluscum contagiosum, a skin infection seen particularly in children.
Despite its name it is not very contagious, but can occur in families.
In adults florid molluscum contagiosum may be an indication of underlying immunodeficiency, as in AIDS patients.
Clinical features
The white, umbilicated papules of molluscum contagiosum are characteristic.
Large solitary lesions may cause confusion as can secondarily infected, excoriated lesions.
These lesions often itch, particularly in patients with atopy.
Resolving lesions may be surrounded by a small patch of eczema.
Diagnosis
Diagnosis is usually based on clinical appearances or microscopy of the contents of papules.
Sometimes there is confusion with viral warts.
Treatment
Most treatments result in discomfort and may not be tolerated by young children.
An antibiotic–hydrocortisone ointment can be used for excoriated lesions.
Treatment with liquid nitrogen is probably the simplest treatment.
Other methods include superficial curettage and carefully rotating a sharpened orange stick moistened with phenol in the centre of each lesion.
Other pox virus infections
The other pox infections are of incidental interest.
Cowpox only sporadically infects cows from its natural reservoir, probably small mammals, and may affect humans.
Papules on the hands enlarge and develop necrosis and crusting.
Milkers’ nodules are due to a virus that causes superficial ulcers in cows’ udders and calves’ mouths.
In humans papules form on the hands and develop into grey nodules with a necrotic centre, surrounding inflammation, and lymphangitis.
A more generalised papular eruption can occur.
is often recognised in rural areas. It is seen mainly in early spring as a result of contact with lambs.
A single papule or group of lesions develops on the fingers or hands with purple papules developing into bulla.
This ruptures to leave an annular lesion 1–3 cm in diameter with a necrotic centre.
There is surrounding inflammation.
The incubation period is a few days and the lesions last two to three weeks with spontaneous healing.
Associated erythema multiforme and widespread rashes are occasionally seen.
Wart viruses
A growing recognition that there is an association between human papilloma viruses (HPV), which cause warts, and cancer has led to a renewed interest in these infections.
The wart is one of the few tumours in which a virus can be seen to proliferate in the cell nucleus.
The different clinical forms of wart are caused by range of HPV, currently divided into over 80 major types.
These viruses are also responsible for cervical cancer and have been associated with squamous carcinomas in the immunosuppressed.
Warts are classed as cutaneous or mucocutaneous.
Epidermodysplasia verruciformis is a rare condition associated with a defect of specific immunity to wart virus.
The following aspects should be remembered:
• Genital warts (due to HPV) very rarely undergo malignant change but HPV infection of the cervix, caused by type 16, frequently leads to dysplasia or in some cases malignant changes.
Cervical smears must be taken.
• Very extensive proliferation of warts occurs in patients receiving immunosuppressive therapy, such as renal transplant recipients in whom wart-like lesions can develop into squamous carcinomas—and in patients with AIDS.
• There is an association between HPV infections of the skin in immunosuppressed patients and the subsequent development of atypical-looking squamous carcinomas.
• Epidermodysplasia verruciformis, an unusual widespread eruption of flat erythematous warty plaques, can also develop into carcinoma.
Treatment
Warts commonly occur in children and resolve spontaneously without treatment or with very simple measures.
These include paints or lotions containing salicylic and lactic acids in various proportions, which should be applied daily.
Salicylic acid (40%) plasters are useful for plantar warts; they are cut to shape and held in place with sticking plaster for two or three days.
Glutaraldehyde solution is also used. For large or painful warts other measures can be used:
• Liquid nitrogen is effective but has to be stored in special containers and replaced frequently.
It can be applied with cotton wool or discharged from a special spray with a focused nozzle.
Freezing is continued until there is a rim of frozen tissue around the wart but not for more than 30 seconds.
Subsequent blistering may occur.
Scarring is unusual.
Carbon dioxide is more readily available and can be transported in cylinders that produce solid carbon dioxide “snow”.
The temperature (about 64°C) is not as low as liquid N2 ( 196°C)
• Heat cautery causes more scarring and requires local anaesthesia. The diathermy loop is effective for perianal warts.
• Curettage and cautery together are effective but leave scars and the warts may recur.
• Podophyllin, 15–25% in tincture of benzoin compound or alcoholic solution, is effective for genital warts when applied each week.
It is, however, toxic when ingested or absorbed, may cause burns, and must never be used in pregnancy. Other treatments include laser therapy, immune enhancement (for example interferon beta), and bleomycin injections. However, relapse is common whatever the remedy. Virus diseases with rashes
Measles and rubella are much less common than previously as a result of widespread immunisation.
However, measles is probably the best known example of an exanthem (a fever characterised by a skin eruption. In an enanthem the mucous surfaces are affected.) Other common clinical patterns can then be compared with it.
All exanthems, except fifth disease (erythema infectiosum), due to RNA viruses.
Measles
• Age. Measles usually affects children, particularly those aged over five years.
• Incubation lasts seven to 14 days. Prodromal symptoms include: fever, malaise, upper respiratory symptoms; conjunctivitis; and photophobia.
• Initial rash. Early on Koplik’s spots (white spots with surrounding erythema) appear on the oral mucosa.
After two days a macular rash appears on the face, trunk, and limbs.
Look behind the ears for early lesions.
• Development and resolution. The rash becomes papular, with coalescence.
There may be haemorrhagic lesions and bullae which fade to leave brown patches.
• Complications are encephalitis, otitis media, and bronchopneumonia.
• Diagnosis. Specific antibodies may be detected; they are at their maximum at two to four weeks.
Rubella
• Age. Rubella affects children and young adults.
• Incubation lasts 14–21 days.
• Prodromal symptoms. There are none in young children. Otherwise fever, malaise, and upper respiratory symptoms occur.
• Initial rash. Initially some patients develop erythema of the soft palate and lymphadenopathy.
Later pink macules appear on the face, spreading to trunk and limbs over one to two days.
• Development and resolution. The rash then clears over the next two days, and sometimes no rash develops at all.
• Complications. The most important complications are congenital defects in babies of women infected during pregnancy.
The risk is greatest in the first month of pregnancy.
• Diagnosis. The diagnosis is made from the clinical signs above. Serum should be taken for antibodies and the test repeated at seven to 10 days.
• Prophylaxis. Active immunisation is routinely available for all schoolgirls.
Erythema infectiosum (fifth disease)
• Age. Erythema infectiosum affects children aged two to 10 years, mainly girls.
• Incubation lasts five to 20 days.
• Prodromal symptoms.
There are usually none, but there may be a slight fever with initial rash.
• Initial rash.
The initial rash is a hot, erythematous eruption on the cheeks hence the “slapped cheek syndrome”.
Over two to four days a maculopapular eruption develops on the arms, legs, and trunk.
• Development and resolution.
The rash extends to affect hands, feet, and mucous membranes, then fades over one to two weeks.
• Diagnosis is made by finding a specific IgM antibody to parvovirus B19.
• Complications. There are no reported dermatological complications but haematological disorders such as thrombocytopenia, arthropathy, and fetal abnormalities may be associated.
Roseola infantum
• Age. Roseola infantum affects infants aged under two years. • Incubation lasts 10–15 days.
• Prodromal symptoms. There is fever for a few days.
• Initial rash. A rose pink maculopapular eruption appears on the neck and trunk.
• Development and resolution. The rash may affect the face and limbs before clearing over one to two days.
• Diagnosis. The condition is diagnosed from its clinical features.
• Complications include febrile convulsions.
Gianotti–Crosti syndrome
• Age. The Gianotti–Crosti syndrome affects children, usually those aged under 14 years.
• Incubation period is unknown.
• Prodromal symptoms. Lymphadenopathy and malaise accompany the eruption.
• Initial rash. Red papules rapidly develop on the face, neck, limbs, buttocks, palms, and soles.
• Development and resolution. Over two to three weeks the lesions become purpuric then slowly fade.
• Diagnosis. The syndrome may be due to a number of virus infections such as hepatitis B.
• Complications. Lymphadenopathy and hepatomegaly always occur and may persist for many months.
Hand, foot, and mouth disease
• Age. Hand, foot, and mouth disease (Coxsackie virus A) affects both children and adults.
• Incubation period is unknown.
• Prodromal symptoms.
Fever, headache, and malaise may accompany the rash.
• Initial rash. Initially there may be intense erythema surrounding yellow-grey vesicles 1–1·5 mm in diameter.
These are mainly distributed on the palms and soles and in the mouth.
Sometimes a more generalised eruption may develop.
• Development and resolution.
Over three to five days the rash fades.
• Diagnosis.
Coxsackie A (usually A16) virus is isolated from lesions and stools.
A specific antibody may be found in the serum.
• Complications are rare but include widespread vesicular rashes and erythema multiforme.
Other infections
Infectious mononucleosis As well as the erythematous lesions on the palate a maculopapular rash affecting the face and limbs can occur.
